The present invention relates to a substantially static resistant polycarbonate composition.
Polycarbonate compositions are the materials of choice for making optical information storage media. Optical information storage media include such articles as compact disks, audio disks, laser disks, optical disk memories and magnetic-to-optical disks to which information may be written and from which it may be read by laser. Such media may be produced from polycarbonates by art-recognized means.
Polycarbonate compositions, prepared by a melt condensation process as disclosed in, for example, U.S. Pat. No. 5,606,008, are becoming the materials of choice in manufacturing compact disks (CDs). Good antistatic performance is critical for polycarbonate compositions used to mold compact disks as well as for other polycarbonate applications where light transmission is critical to performance. High static charge generated during injection molding of compact disks can result in molded parts which will attract dust and compromise the final quality of such disks. High static charge can also result in attraction between disks resulting in situations where disks appear to stick together during the transfer process, e.g. from an injection molder, resulting in stoppage and yield losses during CD manufacturing. For CD applications where a re-writeable substrate is spin-coated onto a disk surface, low static charge is critical for uniform wetting of the re-writeable layer. However, a characteristic of CDs manufactured from polycarbonate made by a melt condensation process, as disclosed in U.S. Pat. No. 5,606,008, is generation of a high negative static charge, typically &lt;-2.0 kV. For the successful use of polycarbonate compositions in making compact disks the CDs preferably must have a static charge between about -2 kV and about +2.0 kV.
Antistatic polycarbonate compositions are disclosed in Japanese Patent Application No. JP62207358. These compositions are used for high-density optical information recording media such as CDs, video disks, etc., and are reported to have suitable antistatic properties. The antistatic agents in these compositions are limited to acidic, partially esterified phosphoric acid derivatives used at the level of 0.01 wt. % to 4.8 wt. % parts based on the polycarbonate.
There is thus a need for a polycarbonate composition, derived from a polycarbonate made by a melt condensation process, which, when used to make CDs, will limit the static charge to between about -2 kV and about +2 kV. There is also a need for a polycarbonate composition containing a non-acidic antistatic agent. There is also a need for a polycarbonate composition containing a reduced amount of antistatic agent. There is further a need for molded articles comprising optical information storage media, particularly CDs, made from said polycarbonate compositions having static charge limited to between about -2 kV and about +2 kV.